Downhole drilling operations commonly require a downhole tool to be actuated after the tool has been deployed in the borehole. For example, underreamers are commonly tripped into the borehole in a collapsed state (i.e., with the cutting structures retracted into the underreamer tool body). At some desired depth (or location), the underreamer is actuated such that the cutting structures expand radially outward from the tool body thereby engaging the borehole wall. Hydraulic actuation mechanisms are well known in oilfield services operations and are commonly employed, and even desirable, in such operations.
For example, one well-known hydraulic actuation methodology involves wireline retrieval of a plug (or “dart”) through the interior of the drill string to create differential pressure to actuate an underreamer. Upon completion of the reaming operation, the underreamer may be deactuated by redeploying the dart. While commercially serviceable, such wireline actuation and deactuation mechanisms are both expensive and time-consuming in that they require concurrent use of wireline or slick line assemblies.
Another commonly used hydraulic actuation methodology makes use of shear pins designed to shear at or above a specific differential pressure (or in a predetermined range of pressures). Ball drop mechanisms are also known in the art, in which a ball is dropped down through the drill string to a ball seat. Engagement of the ball with the seat typically causes an increase in differential pressure which in turn actuates the downhole tool. The tool may be deactuated by increasing the pressure beyond a predetermined threshold such that the ball is urged through the seat. While such shear pin and ball drop mechanisms are also commercially serviceable, they are generally one-time or one-cycle mechanisms and do not typically allow for repeated actuation and deactuation of a downhole tool. Moreover, ball drop mechanisms generally require that the drill string have an unobstructed through bore extending from the surface to the ball seat. As such, ball drop mechanisms are not typically suitable for near bit tool deployments (e.g., tool deployments that are below measurement while drilling “MWD” and logging while drilling “LWD” tools).
There remains a need in the art for a hydraulic actuation assembly that enables a downhole tool, such as an underreamer or a stabilizer, to be actuated and deactuated substantially any number of times during a drilling operation without breaking the tool string and/or tripping the tool out of the borehole.